Conventional deadbolt locks manufactured today are generally of a "Yale" type which have been in active use since their invention in 1865 by Linus Yale. They are well illustrated under the category of "Locks" in typical encyclopedias, such as page 368 of Volume "L" of the 1973 Revision of the World Book Encyclopedia. The basic construction is of a cylinder with a central plug. Several, usually 4 or 5, holes are drilled thru the cylinder into the central plug along a common plane. Driver pins, locking pins, and springs are placed in the holes and retained. The interface between the driver pins and the locking pins are positioned within the central plug. The position therefore of the locking pins in the holes bridging the cylinder and the central plug prevents the central plug from being rotated. This rotation of the central plug is the movement which normally provides the unlocking motion of the locksets.
There is typically a special profile slot along the centerline of the plug to receive an appropriately designed key. The insertion of an appropriately designed key with a specifically ground key profile into the key slot raises each of the driver pins and therefore the locking pins to a point such that the interface between the driver pins and the locking pins is at the cylindrical gap between the cylinder and the central plug. This allows the central plug to be rotated, causing the lock to be "unlocked".
The ability to require 4 or 5 driver pin/locking pin combinations to be at precisely the same height before the central plug can be rotated has historically provided a relatively high degree of security against the lock being opened without a proper key.
In the intervening years since the invention of the Yale lock, other devices have been developed to thwart the security of this type device. Lock picking tools are manufactured and sold to allow a person to unlock a Yale lock without a key. Using these tools, typicaly a slight rotary spring tension is applied by a spring bar to tend to rotate the central plug toward the unlocking direction. A thin pick is then used to individually lift the pins until the interface between the driver pin and the locking pin "catches" at the interface between the central plug and the cylinder. This catching actions is facilitated by microscopic manufacturing differences in the diameters of the individual holes and the diameters of the individual pins. When all of the locking pins are caught at the interface, the spring tension starts the unlocking motion.
In some cases, a pick can be moved swiftly along the key hole and can quickly unlock the lock. This cannot be done on all locks, but when it works, a lock can be unlocked in less than one second. Further, a Lock Gun is sold which looks somewhat like a small pistol. It is inserted into the lock and a trigger pulled. The impact of a bar against the driver pins in combination with the spring tension as mentioned above can in some cases quickly release a lock.
The net effect of these and other devices is that high security locks such as deadbolt locks can be easily and quickly be defeated by persons with small and available tooling.